My previous patents Nos. 4,113,549 issued Sept. 12, 1978, and 4,137,118 issued Jan. 30, 1979, disclose structures of the character described above in which the integral reinforcing ribs are undercut to an I-section to produce maximum efficiency in terms of section modulus and to produce a high strength to weight ratio. Because of ease of fabrication, superior performance, and other attributes, those structures can advantageously be substituted for structures of honeycomb, skin-and-stringer, and integrally machined type.
In certain cases--for example, jet engine compressor housings--structures of the character disclosed in the foregoing patents tend to be resonant at undesirable frequencies in the thin skin areas between the integral reinforcing ribs. Heretofore, these vibrations have been damped or suppressed with various compliant, energy absorbing materials. This solution is undesirable, however, as the energy absorbing material increases both the weight and the cost of the component.